When an object needs to be covered with a piece of flexible material that is to hug its contours, it is generally maintained by means of holding forms adjusted to the object to be covered. This is the case, for instance, in the European patent application No. 0 223 312 that describes the covering of a seat cushion. The primary drawback of the holding forms resides in their characteristic features designed specifically for an object of given sizes and shapes. The manufacturer needs as many forms as there are types of objects to be covered. Furthermore, there are mechanical holding processes, but the latter require generally long setting-up periods and they are ill-suited for automation and cannot be used in cases of complete covering of the object concerned, considering the absence of areas suitable for gripping the latter.